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English definition of “lunacy”

lunacy

noun [U] uk   /ˈluː.nə.sɪ/ us  
stupid behaviour that will have bad results: It would be lunacy to try to climb the mountain in this weather. It was sheer lunacy spending all that money.Of unsound mindStupid and silly old-fashioned mental illnessOf unsound mindStupid and silly
(Definition of lunacy from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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